1. Field of the Invention
The present invention relates to the security of confidential information, and more particularly to the generation of a secret key for encrypting confidential information.
2. Description of the Related Art
Security of confidential information remains a vital concern for those that store sensitive information or transmit sensitive information across both secure and insecure networks alike. Presently, cryptography is the preferred method of securing confidential information. In cryptography, security can be achieved through encryption. Encryption involves the conversion of a clear-text message into a data stream that appears to be a meaningless and random sequence of bits known as cipher text.
A cryptographic algorithm, also known as cipher, is the mathematical function that processes plain text input to produce a cipher text message. The cryptographic algorithm further can be configured to process cipher text messages to produce clear text. All modern ciphers use keys together with plain text as the input to produce cipher text. A key is a value that works with a cryptographic algorithm to produce specific cipher text. The same or a different key can be supplied to the decryption function to recover plain text from cipher text.
There are a number of techniques used to encrypt and decrypt information with passwords. Generally, encryption and decryption approaches can be classified as symmetric and asymmetric in nature. The most common approach for symmetric encryption involves the one-way hashing of a known password. A passphrase hash is a method of transforming a text string that can be remembered by a human user, into a result that can be used either: as an “authenticator”, which can be stored and used at a later time to check whether a user knows the passphrase, and as pseudorandom data for a cipher or secret key. In the latter circumstance, the passphrase hash is referred to as a Password-Based Key Derivation Function (PBKDF). A driving characteristic of symmetric encryption is that symmetric encryption requires that a password be known and remembered. Moreover, the security of symmetrically encrypted data rises and falls with the security of the encryption key.
Keyed hashes—including hash function based message authentication codes—use a secret key in conjunction with a hash algorithm to generate a message authentication code or checksum. A similar technique for generating message authentication codes uses part of the last cipher text block resulting from encrypting the data with a symmetric key algorithm for the same purpose: to generate a checksum of the message that could only be generated by an entity with the secret key. Both of these forms of checksums rely on processing a message with a shared secret key in order to protect against undetected tampering with a message. Both require a shared secret to use and neither generates a secret.
Many public-key based authentication protocols exist, where a first user sends a challenge to a second user. The second user can encrypt the challenge with a private key associated with the second user and the second user can send the encrypted challenge to the first user. The first user can decrypt the response with the public key associated with the second user in order to confirm that the second user possesses a public key for the second user and should be deemed authentic. This general approach is used in secured sockets layer (SSL) technology and in some certificate-based workstation login schemes. The general approach, however, is suitable only for the authentication of a user, and not for the confidentiality of data.